A package used in a surface-mount crystal resonator is constituted by joining a crystal resonator plate to the interior of a box-like container having an opening in the top, and thereafter hermetically sealing the opening with a lid. The container is generally a burning body of ceramics.
In recent years, although microniaturization of various electronic devices is under way, there is a limit to the burning accuracy of a microminiaturized burning body of ceramics. When a burning body of ceramics such as described is miniaturized, ceramic burning displacement becomes apparent, and such burning displacement has influence such as poor hermeticity on the burning body of ceramics. For this reason, burning displacement cannot be ignored.
Currently, Patent Documents 1 and 2 disclose crystal resonators having a configuration in which a container and lids such as described are constituted by a pair of crystal plates, for example, and a crystal resonator plate formed by integrating a resonating portion where an excitation electrode is formed with a frame portion formed along the outer periphery of the resonating portion is sandwiched between the pair of crystal plates, with the joining material in between.
In the crystal resonators according to Patent Documents 1 and 2, the surfaces of the upper and lower lids (pair of crystal plates) and the surface of the crystal resonator plate undergo mirror finishing, and the lids and the crystal resonator plate are joined directly to one another (interatomic bonding). Equipment for implementing interatomic bonding as referred to herein is expensive, so the crystal resonators according to Patent Documents 1 and 2 increase the manufacturing cost.
Patent Document 3 discloses another crystal resonator different from the crystal resonators described in Patent Documents 1 and 2, in which upper and lower lids constituted by a pair of crystal plates and a crystal resonator plate, such as described, are joined directly to one another. In the crystal resonator according to Patent Document 3, the surfaces of the upper and lower lids (pair of crystal plates) and the surface of the crystal resonator plate undergo mirror finishing as in the case of the crystal resonators according to Patent Documents 1 and 2, and are formed as flat smooth surfaces having very little unevenness. Under such surface conditions of the upper and lower lids and the crystal resonator plate, it is difficult to obtain enough joining strength in joining the surfaces of the upper and lower lids and the surface of the crystal resonator plate to the joining material.